Recognition and uptake of free and nanoparticle-bound betalactoglobulin - a food allergen - by human monocytes

Scope: To improve our understanding of the interaction of food allergens with cells of the immune system, the endocytosis by human monocytes of bovine β-lactoglobulin (BLG) and ovomucoid (OM) – two major food allergens – and human serum albumin (HSA) was studied. Methods and results: BLG was covalently conjugated to dextran-coated magnetic nanoparticles (MNPs) without affecting its structure and immunoreactivity. BLG-conjugated MNPs were taken up by human monocytes much more efficiently than non-conjugated MNPs, allowing easy magnetic separation of cells that had adsorbed the allergen. BLG, OM, and HSA were conjugated to MNPs also labeled with a fluorescent probe. The uptake of these materials by human monocytes was monitored through flow cytometry, and compared with fluorescent MNPs and the free fluorescently labeled proteins, confirming higher uptake of the BLG-conjugated MNPs versus non-conjugated MNPs. OM but not HSA conjugation to particles enhanced uptake of the MNPs. Confocal microscopy provided direct evidence of the actual internalization of BLG–MNP conjugates into the cytoplasm. Conclusions: These results contribute to the current understanding of the interaction between food allergens and antigen-presenting cells, and demonstrate that the BLG is readily endocytosed by monocytes both as the single protein and as a conjugate.